Project Summary The presence of chronic physical and medical illnesses contributes significantly to premature mortality in individuals with schizophrenia spectrum disorders (SSDs). Physical inactivity, a modifiable risk factor that impacts all-cause mortality, has been identified as a critical target to improving health and quality of life. Further, cardiorespiratory fitness (CRF), an important health indicator linked with lowered risk of all-cause mortality, is reduced in individuals with SSDs. Despite the well-known benefits of exercise and the known sedentary lifestyle of this population, established and scalable interventions for this population are limited. Given that the majority of exercise interventions developed for individuals with SSDs require access to gym equipment and/or supervision from a trainer, it is unlikely that exercise adoption will occur upon study completion. As a result, our objective is to develop and test the feasibility of an accessible and scalable exercise intervention integrating home-based and group-based walking procedures, activity tracking, goal setting, and stepwise intensity progressions to improve CRF and associated health indicators. The central hypothesis is that an intervention that increases physical activity (PA) as measured by minutes spent walking (at the prescribed intensity) and steps/day will result in improved health and lowered risk for premature mortality as evidenced by superior CRF (primary outcome), and on a variety of secondary outcomes (e.g. blood pressure). Guided by strong preliminary data and grounded in Self-Determination Theory (SDT), this hypothesis will be tested via three specific aims: 1) To develop a manual-based walking intervention for individuals with SSDs: Physical Activity Can Enhance Life (PACE-Life). The manual will include guidelines for goal setting and translating intentions into behaviors (i.e., ?if-then? plans), instructions for the group-based walking activity and home-based walking activity (which includes Fitbits), and increasing exercise intensity in a step-wise manner. 2) To examine the feasibility of implementing PACE-life at a community mental health clinic in an open trial of 14 individuals with SSDs. We will also examine the impact of PACE-life on intermediate targets (autonomous motivation and SDT needs), proximal outcomes (minutes spent walking and steps/day), the primary outcome of CRF, and secondary outcomes. And, 3) To conduct an initial RCT of PACE-life compared to Fitbit Alone (FA) among 56 patients with SSDs receiving treatment in a community mental health center. We hypothesize that, compared to FA, PACE-life will be associated with: a) Improved proximal and primary outcomes including greater minutes/week spent walking and steps/day and increased CRF at mid-treatment (3 months), post-test (6 months), and one-month follow-up; b) Decreases in secondary outcomes including loneliness, SSD symptoms, resting heart rate, and blood pressure at mid- treatment, post-test, and one-month follow-up. And, c) Higher levels of theoretically-relevant, intermediate targets (autonomous motivation and SDT needs) at mid-treatment, post-test, and one-month follow-up.